This invention relates to a process for producing (meth)acrylic anhydride, in particular, to a process for producing (meth)acrylic anhydride as a raw material for (meth)acrylic ester monomer which is usable as a raw material for polymer for semiconductor resist use. This invention also relates to a process for producing (meth)acrylic ester, in particular, to a process for producing (meth)acrylic ester as a raw material for polymer for semiconductor resist use.
As a process for producing (meth)acrylic anhydride, there have been known processes in which (meth)acrylic acid is reacted with (meth)acrylic chloride (Khim. Prom. (Moscow) (1969), 45 (11), 822-3) and in which (meth)acrylic acid is reacted with acetic anhydride and the resultant reaction product is distilled (Japanese Patent Laid-Open No. 62-158237).
The process in which (meth)acrylic anhydride is produced by reacting (meth)acrylic acid with (meth)acrylic chloride, however, involves generating an acidic gas, and therefore, requires a reactor made up of special materials which have a resistance to corrosion. Thus it is not suitable for the production in industrial scale.
On the other hand, in the process in which (meth)acrylic anhydride is produced by reacting (meth)acrylic acid with acetic anhydride and distilling the resultant reaction product, the materials for the reactor is not a problem, but it is hard to purify the (meth)acrylic anhydride into a high-purity product. That is, the distillation, a common purifying process, has a problem that concentrated (meth)acrylic anhydride is very likely to polymerize because it is exposed to high temperatures under an acidic condition in the final stage of distilling step in which (meth)acrylic acid, mixed acid anhydride of (meth)acrylic acid and acetic acid, and unreacted acetic anhydride are distilled off from an intended product.
A process is known in which (meth)acrylic esters are produced from (meth)acrylic anhydride and alcohols; however, this process is not suitable for industrially producing (meth)acrylic ester having the following the formula (3) or (4), which is useful in the electronic material applications, in particular, as a raw material monomer for polymer for semiconductor resist use, because it is hard to produce high-purity (meth)acrylic anhydride as a raw material for the esters, as described above. Specifically, there is a problem that the use of low-purity (meth)acrylic anhydride as a raw material causes a side reaction or a polymerization reaction, resulting in production of low-purity (meth)acrylic esters in low yield. 
In the formula, R1 represents hydrogen atom or alkyl group; n and m represent independently 0 or 1 as the number of methylene group; and R3 represents hydrogen atom or methyl group. 
In the formula, R2 represents alkyl group; and R3 represents hydrogen atom or methyl group.
Accordingly, one object of this invention is to provide a process for industrially producing high-purity (meth)acrylic anhydride, especially (meth)acrylic anhydride used as a raw material for (meth)acrylic ester monomer which is usable as a raw material for polymer for semiconductor resist use, while avoiding polymerization. Another object of this invention is to provide a process for producing high-purity (meth)acrylic ester of a secondary or tertiary alcohol in high yield, in particular, a process for producing high-purity (meth)acrylic ester having the formula (3) or (4), which is a raw material monomer for polymer for semiconductor resist use, in high yield.
The inventors of this invention found that in the process of producing (meth)acrylic anhydride by reacting (meth)acrylic acid with a fatty acid anhydride, high-purity (meth)acrylic anhydride can be obtained by neutralizing the resultant reaction mixture with an aqueous alkaline solution while avoiding distillation, and accomplished this invention.
Specifically, this invention is a process for producing (meth)acrylic anhydride comprising a step of reacting (meth)acrylic acid with a fatty acid anhydride; and a step of neutralization-washing the resultant reaction mixture with an aqueous alkaline solution having a pH of 7.5 to 13.5.
In this process, preferably the above resultant reaction mixture is dissolved in a low-polar solvent prior to the above neutralization-washing step.
The (meth)acrylic anhydride produced in this process is suitable for the raw material for (meth)acrylic ester monomer, which is a raw material for polymer for semiconductor resist use.
Further, this invention is a process for producing (meth)acrylic ester which includes an esterifying step of reacting the (meth)acrylic anhydride produced by the above described process with a secondary or tertiary alcohol in the presence of a basic compound which in 25xc2x0 C. water has an acidity (pKa) of 11 or less.
As the secondary or tertiary alcohol used in the reaction, are preferable alcohols having the following formula (1) or (2), and as the (meth)acrylic ester produced through the reaction, are preferable (meth)acrylic esters having the following formula (3) or (4). 
In the formula, R1 represents a hydrogen atom or an alkyl group; and n and m represent independently 0 or 1 as the number of methylene group. 
In the formula, R2 represents alkyl group. 
In the formula, R1 represents a hydrogen atom or an alkyl group; n and m represent independently 0 or 1 as the number of methylene group; and R3 represents a hydrogen atom or a methyl group. 
In the formula, R2 represents an alkyl group; and R3 represents a hydrogen atom or a methyl group.
When the (meth)acrylic ester thus produced is that expressed by the above formula (3), (meth)acrylic ester with higher-purity can be obtained by adding a washing step of washing the (meth)acrylic ester obtained after the above esterifying step with a low-polar solvent and then with an aqueous acid solution and/or an aqueous alkaline solution.
Further, when the (meth)acrylic ester thus produced is that expressed by the above formula (4), (meth)acrylic ester with higher-purity can be obtained by adding a washing step of washing the (meth)acrylic ester obtained after the above esterifying step with an aqueous alkaline solution and then with an aqueous acid solution. Further, thus obtained (meth)acrylic ester may be subjected to thin-film distillation to provide higher-purity (meth)acrylic ester.
The (meth)acrylic ester produced in accordance with the process of this invention is suitable for the raw material for polymer for semiconductor resist use.
In this invention, (meth)acrylic anhydride is produced by reacting (meth)acrylic acid with a fatty acid anhydride. The term xe2x80x9c(meth)acrylic acidxe2x80x9d, as is commonly used, means a general term for the acrylic acid and the methacrylic acid. Preferably the fatty acid anhydrides used in this invention are compounds having the following structural formula: 
wherein R4 represents alkyl group.
In the above formula, R4 is preferably an alkyl group with 1 to 3 carbon atoms, and the two units of R4 may be different, but preferably they may be generally the same.
The reaction temperature is preferably xe2x88x9230xc2x0 C. to 120xc2x0 C., and more preferably 0xc2x0 C. to 100xc2x0 C. The higher the reaction temperature becomes, the higher the reaction rate becomes, and lower the reaction temperature becomes, the more the side reaction is inhibited. Preferably the reaction is conducted while removing the fatty acid produced as a by-product outside the system under reduced pressure. This reaction can be conducted without a solvent, but an inert solvent may be used depending on the situation. The inert solvents include, for example, n-hexane, toluene and xylene.
A catalyst may also be used for the reaction, if necessary, and the catalysts applicable include, for example, phosphoric acid, potassium acetate and sulfuric acid.
To inhibit polymerization during the reaction, preferably a polymerization inhibitor is appropriately used.
In this invention, the reaction mixture after the reaction step is neutralized with an aqueous alkaline solution havings a pH of 7.5 to 13.5. Preferably, the reaction mixture is dissolved in a low polar solvent prior to this neutralization step. When using a low polar solvent in the reaction, the solvent may remain as it is or may be removed after the reaction.
The low polar solvents applicable are those which can dissolve (meth)acrylic anhydride, are less soluble in water, and are easily distilled off from (meth)acrylic anhydride.
The low polar solvents as above include, for example, hydrocarbon solvents, and particularly preferable low polar solvents include, for example, aliphatic hydrocarbons such as n-hexane, n-heptane and n-pentane; and aromatic hydrocarbons such as toluene. The amount of the solvent used is usually 1 to 30 times the weight of (meth)acrylic anhydride, preferably 5 to 20 times the weight of the same. The larger amount of the low polar solvent leads to the higher effectiveness of the neutralization with an aqueous alkaline solution. The smaller amount of the low polar solvent leads to lowering the cost.
The lower pH value of the aqueous alkaline solution leads less decomposition of (meth)acrylic anhydride. The aqueous alkaline solutions applicable here are not particularly limited to specific ones, and they include, for example, aqueous solutions of hydroxides or carbonates of sodium or potassium. The neutralization-washing is performed at least once and appropriately repeated depending on the amount of the remaining impurities. Excess neutralization-washing leads to loss of (meth)acrylic anhydride, therefore, the neutralization-washing is stopped once the impurities reach the tolerable levels or less.
In an example of the processes of industrially operable neutralization-washing, steps include, by using a container equipped with a mechanism capable of removing the solution from its lower part, filling a solution into the container, adding an aqueous alkaline solution while stirring the mixture, stirring it adequately, allowing the mixture to stand still to occur layer-separation, and removing the water layer (the lower layer).
In the neutralization-washing step, preferably the reaction mixture is washed with water after the washing with an aqueous alkaline solution, depending on the situation.
This neutralization-washing step gives a mixed solution containing mainly (meth)acrylic anhydride and a low polar solvent. The (meth)acrylic anhydride is obtained after concentrating the mixed solution, for example, by distilling off the low polar solvent. At this point, acids such as (meth)acrylic acid have been already removed; therefore, even if the solution is heated, polymerization is hard to induce.
The (meth)acrylic anhydride produced in this manner is suitable for the raw material for (meth)acrylic ester monomer which is a raw material for polymer for semiconductor resist use, since it is low in impurities.
This invention is also a process for producing (meth)acrylic ester in which the (meth)acrylic anhydride produced in this manner is reacted with a secondary or tertiary alcohol in the presence of a basic compound which in 25xc2x0 C. water has an acidity (pKa) of 11 or lower. This process is suitable for producing (meth)acrylic ester having the above formula (3) or (4) from a lactone alcohol having the above formula (1) or an adamantyl alcohol having the above formula (2), as secondary or tertiary alcohol.
In the lactone alcohols having the formula (1), R1 represents hydrogen atom or alkyl group; when R1 is alkyl group, though the number of the carbon atoms is not particularly limited, preferably R1 is a hydrogen atom or an alkyl group with 1 to 5 carbon atoms from the viewpoint of reactivity, ease of purification and polymerizability. Particularly preferably R1 is a hydrogen atom or a straight-chain alkyl group such as methyl group, ethyl group, n-propyl group and n-butyl group.
In the adamantyl alcohols having the above formula (2), R2 is an alkyl group, though the number of the carbon atoms is not particularly limited, preferably R2 is an alkyl group with 1 to 5 carbon atoms from the viewpoint of reactivity and polymerizability, particularly preferably R2 is straight-chain alkyl group such as methyl group, ethyl group, n-propyl group and n-butyl group.
The acidity (pKa) in 25xc2x0 C. water of the basic compound used as a catalyst in this ester synthesizing reaction is 11 or lower, and preferably 6 to 11. As the basic compound, are preferable amines and nitrogen-containing heterocyclic compounds whose nitrogen atoms may be members constituting a ring. Such basic compounds include, for example, triethylamine (pKa=10.72), pyridine (pKa=5.42), 2,6-dimethylpyridine (pKa=6.90), triethylenetetramine (pKa=3.25, 6.56, 9.08, 9.74), triethanolamine (pKa=7.76) and piperazine (pKa=5.59, 9.71).
Preferably the amount of the basic compound used is appropriately changed depending on the type of the secondary- or tertiary-alcohols used in the reaction. When the alcohol as a raw material is a lactone alcohol shown by the above formula (1), the amount is usually 0.1 to 3 mol, and preferably 0.5 to 2 mol per mol of the lactone alcohol shown by the above formula (1). And when the alcohol as a raw material is adamantyl alcohol shown by the above formula (2), the amount used is normally 0.1 to 3 mol, and preferably 0.5 to 2 mol per mol of the adamantyl alcohol shown by the above formula (2).
The lower limit of the reaction temperature in the ester synthesizing reaction is normally xe2x88x9220xc2x0 C. or higher, preferably 10xc2x0 C. or higher, and more preferably 40xc2x0 C. or higher. And the upper limit of the reaction temperature is normally 120xc2x0 C. or lower, preferably 100xc2x0 C. or lower, and more preferably 80xc2x0 C. or lower. The lower the reaction temperature is, the more the side reaction is inhibited.
The reaction time is not particularly limited; however, preferably the time is set to give the largest possible amount of intended product, taking into consideration the ratio of the (meth)acrylic ester produced as an intended product to the decomposition products of secondary or tertiary alcohols. The reaction time is normally 5 to 50 hours, and preferably 10 to 40 hours. The shorter the reaction time is, the more the side reaction is inhibited.
In the ester synthesis, inerts solvent, such as halogenated hydrocarbons, ethers, ketones and aromatic hydrocarbons, may be used, if necessary. In order to inhibit polymerization, preferably a polymerization inhibitor, such as hydroquinone and hydroquinone monomethyl ether, and oxygen are allowed to exist.
When the (meth)acrylic ester obtained in this manner is a highly polar monomer such as the (meth)acrylic ester represented by the formula (3), unreacted (meth)acrylic anhydride can be removed by dissolving the monomer in a polar solvent and washing the same with a low polar solvent as a poor solvent. The solvent used is not necessarily a special one, and the polar solvents applicable include, for example, a water-methanol mixed solvent, water, methanol and ethylene glycol. The low polar solvents applicable include, for example, aliphatic hydrocarbons such as n-hexane, n-heptane and n-pentane and aromatic hydrocarbons such as toluene. When using a water-methanol mixed solvent, methanol can be distilled off from the water-methanol mixed layer and (meth)acrylic ester shown by the formula (3) can be extracted with an appropriate solvent such as ethyl acetate.
There exist basic compounds, such as amine, used as a catalyst and an acid by-product such as (meth)acrylic acid in the extracted solution; therefore, the solution is washed with an aqueous acid solution and/or an aqueous alkaline solution. The aqueous acid solutions applicable include, for example, an aqueous solution of sulfuric acid and the aqueous alkaline solutions applicable include, for example, an aqueous solution of sodium hydroxide. If the pH values of these aqueous solutions are too high or too low, the (meth)acrylic ester shown by the formula (3) is liable to be decomposed; therefore, preferably their pH values fall in the weak-acid or weak-base range with a pH of 4 to 10. Lastly, the extract is appropriately washed with a neutral aqueous solution such as an aqueous solution of sodium chloride.
On the other hand, when the resultant (meth)acrylic ester is a low polar monomer such as (meth)acrylic ester represented by the formula (4), unreacted (meth)acrylic anhydride can be removed by dissolving the (meth)acrylic ester in a low polar solvent as a poor solvent and washing the same with an aqueous alkaline solution. The low polar solvent used is not necessarily a special one, and the low polar solvents applicable include, for example, aliphatic hydrocarbons such as n-hexane, n-heptane and n-pentane and aromatic hydrocarbons such as toluene. The types of the aqueous alkaline solutions used are not particularly limited, and they include, for example, an aqueous solution of sodium hydroxide and an aqueous solution of sodium hydrogencarbonate. There exists a basic catalyst, such as amine, in the (meth)acrylic ester having been washed with an aqueous alkaline solution, therefore, the solution is washed with an aqueous acid solution. The aqueous acid solutions used are not particularly limited, and they include, for example, an aqueous solution of sulfuric acid. If the pH value of the aqueous acid solution is too low, the (meth)acrylic ester shown by the formula (4) is liable to be decomposed; therefore, preferably its pH value falls in the weak-acid range with a pH of 4 or higher. Lastly, the solution is appropriately washed with a neutral aqueous solution such as an aqueous solution of sodium chloride.
If the (meth)acrylic ester shown by the formula (3) or (4) thus obtained is subjected to thin-film distillation, the metal impurities can be reduced to 50 ppb or less. The thin-film evaporator used here is not necessarily a special one, a commonly used one is applicable. Preferably this thin-film distillation is carried out at 100 to 200xc2x0 C. under 1 to 1500 Pa.
The (meth)acrylic ester thus produced contains less impurities, and therefore, it is suitable for (meth)acrylic ester monomer used as a raw material for polymer for semiconductor use.